Molecular view of polymer/water interfaces in latex paint

To obtain a molecular level view of the interface of a latex particle with water solvent, atomistic simulations using two different force fields were performed for a slab of methyl methacrylate (MMA)/n-butyl acrylate (BA) random copolymer in water. The carbonyl groups at the polymer/water interface were found to orient significantly toward the water phase. We calculated the copolymer/water and the copolymer/vacuum interfacial tensions, and predict a contact angle for water on copolymer of 77°, consistent with experimental values. We also calculated bulk densities of MMA/BA copolymer, and PMMA and PBA homopolymers, which compare well with experiment, and the structure factor for PMMA, which agrees with neutron scattering results. The simulated T_g of PMMA is not far from its experimental value, despite the much shorter chains and faster cooling rates of simulations versus experiments, because these two effects tend to cancel each other. When we correct for these effects, the predicted T_g is within 5 K of the experimental value.